Self-locking internally threaded fastener &amp; method of manufacture

ABSTRACT

The present invention is directed to an internally threaded prevailing-torque type self-locking fastener which employs a patch of fused thermoplastic material as the locking element and which satisfies the functional torque requirements of both IFI 100/107 (1987) and IFI 101 (1987). In accordance with the present invention the fastener comprises a metal body having a bore extending to its opposing ends, the bore having a threaded surface; a patch of polymeric material applied and fused to a portion of the threaded surface; and the fastener meeting the prevailing-torque characteristics specified in both IFI 100/107 (1987) and IFI 101 (1987). The invention is also directed to a process wherein an internally threaded fastener is processed by first applying and fusing a polymeric resin material to at least a portion of the fastener&#39;s threaded surface and thereafter conditioning the frictional properties of the fastener such that its prevailing torque performance characteristics meet both IFI 100/107 (1987) and IFI 101 (1987).

BACKGROUND OF THE INVENTION

[0001] The present invention relates generally to threaded fastenersand, more particularly, to internally threaded prevailing-torque typeself-locking fasteners and a method for their manufacture.

[0002] Prevailing-torque self-locking fasteners are well known in theart. These fasteners are frictionally resistant to rotation due to aself-contained prevailing-torque feature, often called a “lockingelement.” A variety of different prevailing-torque fasteners are known,including so-called “all metal” fasteners and “plastic patch,” “plasticstrip” or “plastic pellet” fasteners. As their respective names imply,these fasteners achieve a self-locking or prevailing-torque function dueto the characteristics of the particular locking element employed.

[0003] The present invention is directed only to prevailing-torque type,self-locking fasteners that employ a patch of thermoplastic material asthe locking element. Moreover, the invention is directed to internallythreaded fasteners. Such patch type internally threaded self-lockingfasteners are well known in the art and a variety of machines andprocesses for their manufacture are also known, as disclosed, forexample in U.S. Pat. Nos. 3,858,262; 3,894,509; 3,995,074; 4,054,688;4,060,868; 4,100,882; 4,366,190; 4,775,555; 5,141,771; 5,221,170;5,511,510; 5,620,520; and 5,718,945. The disclosures of these listedU.S. Patents are incorporated herein by reference.

[0004] It is known that a large market exists for internally threadedself-locking fasteners having relatively stringent functionalspecifications. That is, the torque required to achieve a particularclamp load between mated internally and externally threaded fastenersmust be no more than a specified maximum, while the torque required todisengage the mated fasteners must exceed a specified minimum. TheIndustrial Fasteners Institute (“IFI”) has promulgated standardsrelevant to such specifications. For example, IFI 100/107 (1987) definesa maximum installation torque that cannot be exceeded and minimumremoval torques (both for the first and fifth removals) that must beexceeded. Similarly, IFI 101 (1987) also defines a torque window—bothminimum and maximum—that the torque for a specific fastener must meet.Such fasteners, used typically in the automotive industry andparticularly on large over highway trucks, have been conventionallyfabricated as all-metal, self-locking fasteners, where the lockingelement is in the form of distorted threads or a distorted metal body.These all-metal, self-locking fasteners have created numerous problemsin the trucking industry. Typically, the distorted thread conceptrequires a cadmium plating but even here, when driven into an assembly,there is a metal to metal galling effect that takes place resulting invarying installation torque levels which, in turn, lead toover-tightening or under-tightening and, therefore, in lost productiondue to replacement of faulty joints. If the cadmium plating is replacedwith other platings, typically zinc, the conditions are exacerbated.Much higher clamping torques are required to attain the same clamploads.

[0005] All-metal locknuts also remove or damage the protective coatingon the mating external threads; thus, resulting in bare metal exposureto the elements with the end result being oxidation or rusting effects.Additionally, over torquing sometimes causes the nut to be driven intothe frame assembly resulting in scarring or scraping to the affectedarea, which requires removal of the assembly, reworking the damaged areaand reinsertion back into production. This results in lost production,higher assembly costs and poor quality.

[0006] The plastic patch type, self-locking internally threadedfasteners of the present invention eliminate the above problems bymeeting, or even exceeding, the IFI torque requirements ofspecifications 100/107 and 101 for all-metal cadmium plated nuts-evenwhen the fasteners are zinc plated. Additionally, the self-lockingfasteners of the present invention provide improved functionalperformance with a fastener that is lighter in weight and lower in costthan a corresponding all-metal locknut.

SUMMARY OF THE INVENTION

[0007] The present invention is directed to an internally threadedprevailing torque type self-locking fastener which employs a patch offused thermoplastic material as the locking element and which satisfiesthe functional torque requirements of both IFI 100/107 (1987) and IFI101 (1987).

[0008] In accordance with the present invention the fastener comprises ametal body having a bore extending to its opposing ends, the bore havinga threaded surface; a patch of polymeric material applied and fused to aportion of the threaded surface; and the fastener meeting theprevailing-torque characteristics specified in both IFI 100/107 (1987)and IFI 101 (1987).

[0009] The invention is also directed to a process wherein an internallythreaded fastener is processed by first applying and fusing a polymericresin material to at least a portion of the fastener's threaded surfaceand thereafter conditioning the frictional properties of the fastenersuch that its prevailing torque performance characteristics meet bothIFI 100/107 (1987) and IFI 101 (1987).

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The novel features which are characteristic of the invention areset forth in the appended claims. The invention itself, however,together with further objects and attendant advantages thereof, will bebest understood by reference to the following description taken inconnection with the accompanying drawings in which:

[0011]FIG. 1 is a schematic diagram illustrating the sequence of processsteps used in accordance with a preferred embodiment of the presentinvention;

[0012]FIG. 2 is a perspective view illustrating an example of aself-locking nut having an applied plastic patch on its threaded surfaceand a preferred patch applicator used in the practice of the presentinvention, with the nut having been rotated 180° after patch applicationto show the patch location within the nut;

[0013]FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 2;

[0014]FIG. 4 is another cross-sectional view taken along line 4-4 ofFIG. 3;

[0015]FIG. 5 is a cross-sectional view taken generally along the axialcenter line of the applicator illustrated in FIG. 2; and

[0016] FIGS. 6-10 are illustrations of another preferred embodiment of apatch applicator useful in the practice of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The basic component of the present invention is aninternally-threaded fastener fabricated from a metal or metal alloy. Thefastener has a body 10 with a bore 12 extending to its opposing ends 14and 16. The body 10 can be fabricated from any well known metal and may,optionally, be plated with zinc, cadmium or other materials to provideanti-corrosion properties or improved aesthetics. Typically, the bore 12is threaded along its entire length, with the exception of a shortcounter sink at each end, thereby forming a threaded surface 18,terminating with so-called “lead threads” at ends 14 and 16.

[0018] The locking element is in the form of a patch 20 of thermoplasticmaterial applied and fused to at least a portion of the threaded surface18. Most preferably, the patch 20 is well defined and generallyrectangular in shape, with little or no incidental polymer depositslocated outside the main body of patch 20. Thus, the lead threads atboth ends of the fastener will be substantially free of polymerdeposits, facilitating the initial engagement of the fastener with itscomplimentary mating male fastener. A wide variety of plastic materialsmay be employed in the practice of the present invention. However, anylon thermoplastic resin has been found particularly useful. Forexample, nylon 11 supplied by the Morton Powder Division of Rohm andHaas Company under the trade names Corvel 76-5001 or Corvel 76-5004 havebeen found satisfactory.

[0019] The nylon patch locking element 20 is applied and fused to thethreaded surface 18 of the fastener using any of the well knowntechniques disclosed in the prior art, such as those disclosed inseveral of the above-listed patents. Typically, the fastener ispreheated, using an induction coil heater and then an air-entrainedstream of nylon powder is directed onto its threaded surface 18. Thepowder thereby melts and forms a generally molten mass on a portion ofthe threads which, upon cooling, forms a solid plastic patch fused tothe threaded surface.

[0020] One such processing system is illustrated in FIG. 1. As shown,the fasteners 10 are fed from a feed bowl 30 down an escapement track32, through an induction coil heater 34 and into a spray station havingtwo powder applicators 36, 38. The first applicator 36 directs a firstair-entrained powder stream onto the threaded surface of the fastener,and the second applicator 38 directs a second air-entrained powderstream over the first applied powder. It has been found advantageous tobuild the patch with multiple, at least two, powder spray applications.This allows better control of patch coating weight, patch definition andincreased production. The fasteners then proceed onto a conveyor 40where they are air-cooled for a short time, from about one to fiveminutes, and then immersed in a conditioning bath 42. The fasteners arecooled, either in ambient air or by passage through a forced-air coolingchamber, to maintain the temperature of the conditioning bath below 212°F. Conveyor 44 carries the fasteners through bath 42 and deposits themonto still another conveyor 46 which carries the fasteners through aninfrared drying oven 48 and ultimately drops the fasteners into anysuitable shipping or storage container 50.

[0021] In accordance with one preferred embodiment of the presentinvention, the applicator employed to form and direct the air-entrainedpowder into the fastener is that illustrated in FIGS. 2 and 5. Theapplicator 50 comprises a spray head or nozzle 52, forming a generallyarcuate, radially opening slot which is supplied with a pressurized airstream carrying the air-entrained nylon powder via conduit 54. While thearcuate extent of the spray nozzle 52 may be varied, it has been foundthat an arcuate slot in the range of about 60°-75° is preferred, with anarc of about 68° being found optimal. A cylinder 56 is mountedconcentrically around conduit 54, the cylinder having a closed end 58and an open end 60 located immediately adjacent nozzle 52. Thesecomponents thereby define a generally annular vacuum nozzle 62 connectedto a vacuum source via port 64.

[0022] The nylon powder may be delivered to the threaded surface 18 ofthe fastener with the nozzle 52 located at a fixed axial position withinbore 12. However, unexpected advantages have been obtained by applyingthe powder while the nozzle 52, together with vacuum nozzle 62, movesaxially within bore 12. Most preferably, the powder is applied while thenozzles 52 and 62 move axially first in one direction and then in theopposite direction along only an interior portion of the bore 12. Thispowder application technique has been found to substantially reduce thevariance in prevailing-torque performance values that otherwise occurwith a stationary nozzle, depending upon the angular orientation of thenozzle relative to the start point of the fastener's lead threads.

[0023] Another applicator mechanism is illustrated in FIGS. 6-10. Here,two applicators 62 and 64 are mounted in a base block 66. Theapplicators each include a central conduit 68, terminating in a powderspray nozzle 70 with dispensing slot 71. A cylinder 72 is mountedconcentrically around conduit 68 and has a radial cut at its free endwhich forms a vacuum slot 74 when the spray nozzle 70 is mounted overit. Both the spray nozzle slot 71 and the vacuum slot 74 define an arcof about 68°. The block 66 includes passageways 76 for transmission of acoolant (as indicated by the arrows) and vacuum ports 78 whichcommunicate with the interior of cylinder 72.

[0024] As mentioned previously, the fasteners made in accordance withthe present invention achieve the prevailing-torque performancecharacteristics of both IFI 100/107 (1987) and IFI 101 (1987). Theability to meet both the clamp load torque window and minimum removaltorques specified in these IFI standards results, in part, from a postpatch application treatment which conditions the frictional propertiesof the nylon patch locking element and the threaded surface of thefastener, as well. Preferably, the fastener with the pre-applied patchis immersed, sprayed or otherwise effectively wetted with a waxcontaining aqueous emulsion. In the process illustrated schematically inFIG. 1, this conditioning treatment is carried out by immersion of thefasteners in bath 42. While a variety of natural or synthetic waxes maybe employed, a bath comprising an aqueous hydrocarbon wax dispersion hasbeen found satisfactory. One suitable hydrocarbon wax dispersion ismanufactured under the trade designation OKS 1765 by OKS SpecialtyLubricants International GmbH P.O.B. 50 04 66, D-80974 Munich, Germany.A mixture of about 15% to about 30%, and preferably about 20% (byvolume) of OKS 1765 in water, works well in the practice of the presentinvention. The fasteners are thoroughly wetted with the solution andthereafter dried in any conventional manner.

[0025] Of course, it should be understood that various changes andmodifications to the preferred embodiments described herein will beapparent to those skilled in the art. Such changes and modifications canbe made without departing from the spirit and scope of the presentinvention and without diminishing its attendant advantages. It is,therefore, intended that such changes and modifications be covered bythe following claims.

We claim:
 1. A prevailing-torque internally threaded fastenercomprising: a metal body having a bore extending to opposing ends of thebody, said bore including a threaded surface; a patch of polymericmaterial fused to at least a portion of the threaded surface; and saidfastener having prevailing-torque performance characteristics meetingboth IFI 100/107 and IFI 101 standards.
 2. A method of manufacturing aprevailing-torque internally threaded fastener comprising the steps of:providing a metal body having a bore extending to opposing ends of thebody, the bore including a threaded surface; applying and fusing apolymeric resin to at least a portion of the threaded surface; andconditioning the frictional properties of the fused polymeric resin andfastener such that the prevailing-torque performance characteristics ofthe fastener meet both IFI 100/107 and IFI 101 standards.
 3. Thefastener manufacturing method of claim 2 wherein the polymeric resin isapplied to the threaded surface by directing an air-entrained powderedresin stream onto the threaded surface.
 4. The fastener manufacturingmethod of claim 3 wherein the fastener threaded surface is heated priorto application of the resin.
 5. The fastener manufacturing method ofclaim 3 wherein the fastener is zinc plated.
 6. The fastenermanufacturing method of claim 3 wherein a plurality of air-entrainedresin streams are sequentially directed onto the threaded surface. 7.The fastener manufacturing method of claim 3 wherein the air-entrainedresin stream is directed onto the threaded surface while the stream ismoving axially within the bore relative to the body.
 8. The fastenermanufacturing method of claim 7 wherein the air-entrained resin streammoves axially in one direction and then in the opposite direction whilethe resin is applied to the threaded surface.
 9. The fastenermanufacturing method of claim 3 wherein the air-entrained resin streamis directed onto the threaded surface by means of an axially extendingapplicator having a radially opening nozzle at its free end and a vacuumport disposed adjacent the nozzle.
 10. The fastener manufacturing methodof claim 2 wherein after application to the threaded surface, the resinis subjected to a conditioning treatment by wetting the resin with a waxcontaining aqueous emulsion.